Prices for natural gas and electricity have risen over the years, and many consumers desire machines with more energy efficient heat sources. In addition to lowering prices paid for energy, the demand for more energy efficient heat sources is driven by consumers who are worried about conserving finite fossil resources, and lowering carbon emissions.
The EPA and Energy Star have issued new guidelines in June 2014 for a clothes dryer Energy Star certification. Few clothes dryers have achieved this certification. A dryer purchased in 1960 may use the same amount of energy as a current 2014 model, regardless of the make or model. For a dryer to achieve an Energy Star rating, the dryer may be required to reduce current energy use by twenty percent (20%) and the cycle to dry clothes must be no more than 80 minutes on a cycle to dry clothes.
Most current style electric dryers use resistance style/type heating elements with 5000 to 6000 watts at 220 volts. These heating elements may burn bright cherry red at the element itself and heat to a temperature in excess of 2200 degrees F. Most gas dryer work on the same principal by supplying a massive amount of heat (roughly 25000 BTU) to the dryer drum. Both electric and gas dryers may use thermostats to control the temperature inside the drum of the dryer. Many current dryers maintain a drum temperature of around 140 degrees F. The heating element is continually cycled on and off to maintain that optimum temperature inside the drum containing the clothes. The backs of most current dryers have little heat insulation material and a significant amount of heat energy, not utilized in the drying process, is exhausted out. Heated air is not recirculated. Approximately 80% of all dryers manufactured in the United States are electric.
As can be seen, there may be an ongoing need to raise the efficiency of heating sources for machines in general, and electric clothes dryers in specific.